Best Practice for Videoing
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CHECK THE FOLLOWING BEFORE VIDEOING
Camera choice and connecting to the computer
Many different types of cameras have emerged in the last few years. DVD and High Definition cameras are evolving but still have their limitations. Siliconcoach software is optimised for Digital Video (DV). DV video is still the best option for analysing movement. It has the best practical combination of 50/60 images per second and good resolution per image.
The Mini DV cameras and have a DV plug (also known as IEEE, 1394 or iLink). This means you must use a Firewire cable to connect your camera to your computer.
Note, this is not a USB cable. Although you probably got a USB cable in the camera box and you MAY get a video feed from a camera into the computer using a USB connection, the quality is much lower and will probably cause the software to crash.
For more detail on this please see the Hardware section and the Cameras and Image Quality section of the FAQ’s.
- The camera is one of the key components of the system and as such setting up the camera is very important. If you capture poor video there is very little the software can do to improve it so you are left with an unclear or distorted image that will greatly decrease your accuracy.Modern cameras are very good at automatically adjusting to different light conditions but there are a few of things you can do to improve the image quality.
The concepts are similar for all makes of MiniDV cameras and there are examples for a Sony MiniDV camera in this section. However, please always refer to your camera manual as your primary reference.
Shutter:
A fast setting means the shutter is only open for a very short time; this means there is less subject movement while the shutter is open and therefore less blurring. If your image is blurred it is not a function of the software but a function of the camera settings and lighting (you cannot correct for blurring in the software). However, the disadvantage of a fast shutter is that there is less time for light to get onto the camera sensor and this causes dark images. To compensate for this you need lots of light as described in the Lighting section below.
Some cameras use a setting called Sports Mode instead of a manual shutter setting. Sports Mode gives you the fastest shutter speed it can for the given light, therefore to increase shutter speed you need to increase the light.
The Sony cameras use this Sports Mode feature. To set the Sports Mode on the Sony cameras do the following:
1. Connect the power to the camera and turn the camera on.
2. Open the touch screen so you can see it.
3. Press ‘FN’ on the bottom right of the touch screen.
4. Select MENU from the list of options on the Home Screen.
5. Select the menu titled MANUAL SET by pressing the EXEC button.
6. Press EXEC again to select the top option called PROGRAM AE.
7. Use the arrow button on the touch screen to highlight SPORTS and press the EXEC button to select it.
8. Press the RET button twice to get back to the Home Screen and then press the ‘X’ in the upper right of the screen to close the Home Screen.
9. See your camera manual for more details.
Focus:
The focus control is usually able to be set to manual or automatic. Automatic will usually work fine except when someone walks between the camera and the filming area and thereby changes the focus for an instant. This may occur if you have your camera mounted some distance from the subject, such as across a walkway. In these circumstances it is better to set it to manual and then manually adjust the controls to get a clear image.
See your camera manual for more details.
Demo mode:
Demo mode usually starts up about 10 – 20 minutes after starting the camera and you will see the screen start to do all sorts of strange things. For example it may start shaking, the image make go black and white, then sepia, then blurry, then shake again and so on. You do not want this happening when trying to video a subject but unfortunately most cameras come with the Demo mode turned on.
To turn off Demo mode on the Sony cameras do the following:
1. Press ‘FN’ on the bottom right of the screen.
2. Select MENU from the list of options on the Home Screen.
3. Scroll down the list using the down arrow at the bottom until you get the menu titled SETUP MENU and select it by pressing the EXEC button.
4. Scroll down again until DEMO MODE is highlighted and press EXEC again.
5. Use the arrow button on the touch screen to highlight OFF and press the EXEC button to select it.
6. Press the RET button twice to get back to the Home Screen and then press the ‘X’ in the upper right of the screen to close the Home Screen.
7. See your camera manual for more details.
White balance:
Our eyes are very good at adapting to different lighting conditions such that when there are many shades of near-white we perceive them as pure white. Cameras however are not so accommodating and different light conditions such as outdoor, fluorescent, halogen, all give slightly different shades of near white. Sometimes the video images look yellower (warmer) or bluer (cooler). Your camera probably has auto adjustment to accommodate for this but you can help it by telling it if the video situation is indoor or outdoor.
To set the White balance on Sony cameras do the following:
1. Press ‘FN’ on the bottom right of the screen.
2. Select PAGE 2 from the list of options on the Home Screen and then select WHT BAL from the next list.
3. Select INDOOR by pressing on it and then press OK to close that screen.
4. Press the ‘X’ in the upper right of the screen to close the Home Screen.
5. Determine if INDOOR or OUTDOOR gives the best image and set the camera accordingly.
6. See your camera manual for more details.
Recording choice:
You can capture your action two ways using a MiniDV camera. You can capture live. This is the fastest way to get your clips into your computer; however, it does require someone operating the computer and can be more disruptive to the session. Sometimes it is just not practical to have a computer outside or in the training area so your best option is to record to tape and capture it later.
You can also capture from tape. As you don’t have to worry about the capture process this is a less stressful option for those new to video analysis. Just put a tape in the camera and set it to record and forget it. The disadvantage of this method is that you have to go back through the tape and find and capture the segments you want. The Pro software gives you tools to control the camera but this still can be a time consuming process.
- Camera angle:
Make sure you work out which angle will the event/s of interest be best captured. The plane of movement will need to be perpendicular to the camera if you intend to make measurements from the movie. You also need to decide if the whole event be captured without panning the camera. Panning introduces perspective errors that will make any measurements of speed or distance over a time period inaccurate.Camera height:
Generally the camera should be at approximately half the height of the movement of interest. If you are looking at the whole body it would be about hip height, although for a tennis or volley ball serve it would be higher as the athlete will have theri hand above their head. If you were just looking at the lower limbs, the camera should be about knee height.
Camera orientation:
The camera must be level and at right angles to the subject. The cameras must be level in all planes. When you use the drawing tool to draw a horizontal line it assumes the background is also horizontal. You could quite happily make measurements and draw reference lines on the screen, but if the image in the background is not correctly aligned with the camera your conclusions will be wrong. The camera must be:
Scale:
If you want to take distance or speed measurements off the video you will need an object of a known length (calibration scale) in the same plane as the movement and the same distance from the camera as the movement.
Subject’s attire:
Is the person being videotaped wearing clothing that will obscure their actions or limb end point positions? This may be floppy tops, long baggy shorts and skirts or long hair, which could be tied up or taped down.
Background:
It is important that the background the camera sees is as neutral as possible; do not use any thing reflective such as glass. A plain grey, blue or green background is best, try to avoid black or white as they create a lot of contrast and may make your image too dark or too light. Also try to avoid a lot of activity in the background (eg other athletes, crowds, roadways etc), it will cause confusion and make it harder to find the key points on the body.
Computer position:
A desktop box can be securely hidden away under a bench but you will need space on top for the screen, keyboard and mouse. You may also need a space for your tools.
Computer screen position:
The computer screen position is very important as it is not only used for your analysis but also to convey your results and thoughts to the subject. It is critical that they can see the screen and see what they did and what you mean with your feedback.
Keyboard and mouse position:
The keyboard and mouse position needs to be within easy access as you will be using them a lot, especially the mouse. Video analysis is VERY hard using anything other than a mouse.
Cables:
Cables can be dangerous and where possible, cables should be secured and covered with a rubber mat or something similar. You will need power cables and long Firewire cables (these connect the camera to the computer).
- Lighting is a critical and often overlooked part of your setup. The quality of the light greatly influences the quality of your image. The software cannot compensate for bad video. A blurred image is usually the result of incorrect camera settings, bad lighting, or both.Type of lights:
You need lights that do not flicker as the image will flicker on the video clip as well. Fluorescent lighting can cause a lot of flickering. You also need lights that shine as closely as possible to white light, some lights shine light with a yellow or a blue tinge. You may still get good images for analysis but everything may look a bit yellow. It is important not to mix your lights, if you do the Auto Brightness feature on the camera will not be able to compensate for the different shades of ‘white’ emitted from the different lights.
Position:
The lights need to create a diffuse lighting pattern that does not create shadows or light burn (where the lights cause parts of the skin to look ultra white on the video). You will need lights shining directly on the fitting area and also indirectly on the area by bouncing the light of the roof, walls etc. If you are in doubt about what you should do you should contact your local photography or video expert.
Intensity:
Good lighting does not always mean the most intense lights; a few well placed lights positioned as outlined above can work just as well. Intense lighting will cost more in power, create harsh contrasts in the video image and will also create a lot of heat in the area.
Reflection:
Be careful not to have any lights shining on highly reflective surfaces; it causes very bright spots on the video image and the camera will darken the whole image to try and reduce the light ‘burn’.
Power:
You will need power to the computer and monitor but also remember the cameras also need power and could be 2-5 m away from your computer and power box. You must be careful running power cables across an area where people are going to walk.
CHECK THE FOLLOWING DURING VIDEOING
Continue to monitor all the points mentioned above
Check you have a scale in the same ‘space’ as the athlete.
As the people/objects being videotaped change, a chalkboard or piece of paper with the name of the new person/object should be displayed in front of the camera. This allows someone who is unfamiliar with the people/objects to identify them.
If filming multiple trials of a subject, be sure to indicate the trial number by showing numbered pieces of paper or having the subject hold up the proper number of fingers.
Complete a filming record that includes all relevant information. This information may include name, standing height, reach height, weight, age, skill level, type of equipment used, and any other information that may be of use at a later date.
